ACCELERATION EFFECTS ON ELECTRON TUBES 1221 



MIL-E-IB Bump Tester 



This is one of the earliest devices employed for shock testing of tubes 

 under controlled conditions. In order to assure uniformity of results the 

 MIL specifications give its physical dimensions. Fig. 10 illustrates the 

 tester and its method of use. The magnitude of the shock and its duration 

 is given by tube weight, shape of tube envelope contacted by the ham- 

 mer, resilience of rubber pad on the hammer, and the angle (6) through 

 which the hammer is permitted to swing before striking the tube. 



Although for the performance of the tests, only the angle (6) is speci- 

 fied, the shock characteristics of this device have been investigated,^*^ so 

 that shock magnitudes and durations for any tube may be computed 

 from the parameters given above. A typical acceleration time curve is 

 sho^vn in Fig. 11. The simple bell shaped outline of the accelerogram is 

 given by the non-linear spring characteristic of the rubber pad and the 

 generally cylindrical shape of the tube envelope. 



Shock Testing Mechani&m per ASA-C39.3 



This mechanism is also used to check and compare the resistance of 

 tubes to mechanical shocks of predetermined magnitude and duration. 

 In this device the sample to be tested is rigidly fastened on a platform. 

 A steel leaf spring supported at both ends is attached underneath this 

 platform. The test on the sample is performed by raising the platform 

 to a certain height, allowing it to fall on a steel anvil, and then catching 

 it on the rebound. 



The shock magnitude is given by 



G max = 

 and its duration by 



2hk 

 W 



V 12K9 



12Kg 



where W = tableweight (lbs.) 



h = height of fall (inches) 



K = spring constant of leaf spring. 

 A number of leaf springs are available to produce the desired shock 

 characteristics. A full discussion of this mechanism and its performance 

 are covered in Reference 11. A slightly modified version of the tester, 

 used by the Laboratories, together with a typical shock pulse, is sho^vn 

 in Figs. 12 and 13. It can be seen that the pulse is essentially of sinus- 

 oidal shape with higher frequencies superimposed on it. The fundamental 

 frequency is produced by flexing of the leaf spring during its contact 



